Revolving cam electrical switches



United States Patent 3,328,549 REVOLVING CAM ELECTRICAL SWITCHES HenryGeorge Rossini, Scotia, N.Y., and Samuel Paul Jones, Erie, Pa.,assignors to General Electric Company, a corporation of New York FiledFeb. 28, 1966, Ser. No. 530,266 12 Claims. (Cl. 200-166) This inventionrelates to revolving cam electrical switches and more particularly to anew and improved cam arrangement therefor to provide electrical switchesof such type which are especially adapted for high voltage applications;i

While the cam arrangements ofthis invention have utility in a widevariety of switching apparatus, they are especially suited for use'inrailway vehicle circuit controllers and will be particularly describedin that connection. The use and operation of circuit controllers of suchtype are described in U.S. Patents Nos. 2,566,898 and 3,034,031, forexample.

Electrical circuit controllers for use in rail rapid transit equipment,for example,,are usually reversible motor driven revolving-camelectrical switches having a plurality of switch positions to controlmotor-power switching for series-parallel operation of the vehicletraction motors as well as to provide for coasting and braking. In suchswitches a plurality of cams and appropriate cam spacers constructed ofan electrically insulating material are arranged on a camshaft of steelor the like to be driven thereby so that engagement of the cams with theactuating means of appropriate switch means or contactors causesoperation of such devices in a desired sequence. The contacts of suchdevices are usually made from an electrically conductive material, suchas copper. Often, a large potential difference may exist betweenadjacent contactors so that it is necessary that such contactors beelectrically isolated from each other. For many applications, this canbe satisfactorily accomplished by merely providing cams and cam spacersof a suitable electrically insulating material. Because of the relativemovement of the switch parts on each other when actuated by the cams,particles'of electrically conductive material, usually particles ofcopper from the contacts, tends to coat the side surfaces of the camswith a film which is electrically conductive. This conditionisaggravated when the electrical switch is operated in a dirty, oily orotherwise contaminated environment. Under such operating conditions theoil or other contaminants may mix with the con ductive dust to form anelectrically conductive fluid which tends to creep down the'sidesurfaces of the cam toward the cam shaft. Since in the vast majority ofapplications the-camshaft'is at ground potential,-this conductive fluidmay establish a conductive path between the electrical contacts andground through the camshaftto'rfesult in possible damage to theequipment and certain disruption in operation of the circuitsbeingcontrolled.

v Prior'artattempts to overcome this difliculty such as by the provisionof larger diameter cams, tightly pressing adjacent cams and/ or camspacers together or attempting to hold closer manufacturing toleranceshavehot been entirely satisfactory, especially for'switches' for thehigher voltage applications. None of the prior art arrangements of whichwe are aware capable of utilizing individual ca'm elements have beencapable of positively preventing the eventual establishment of such anelectrically conducting path.

7 Therefore, it is an object of this invention to provide a new andimproved cam arrangement for revolving-cam electrical switches whichovercomes one or more of the foregoing prior art difl'iculties and iscapable of operation at much higher voltages.

Patented June 27, 1967 It is another object of this invention to providea new and improved cam arrangement for a revolving-cam electrical switchwhich inherently and positively prevents establishment of anelectrically conductive path to .the camshaft between adjacent cams.

Briefly these objects are obtained in a cam arrangement wherein apositive sealing means is provided between adjacent cam element faceswhich effectively blocks creepage of conductive media down thecamele'ment face to the shaft thereby preventing short circuits andconcurrent damage to equipment.

As used throughout the specification and in the appended claims the termcam element is intended to include cams as well as any spacers which maybe disposed adjacent thereto.

The subject matter which is regarded as our invention is particularlypointed out and distinctly claimed in the appended claims. Ourinvention, however, both as to its organization and method of operation,together with further objects and advantages thereof, is best understoodwith reference to the following description taken in can junction withthe accompanying drawings in which:

FIGURE 1 is a cross section view of a cam arrangement according to oneform of the present invention, and

FIGURES 2 and 3 are cross section views of cam arrangements according toanother form of this invention.

Referring now to FIGURE 1 according to one form of this invention acamshaft 1 is illustrated having a plurality of cam elements thereon. Asshown the arrangement includes four arbitrarily placed cams 2, 3, 4, and5, and three cam spacers 6, 7 and 8 separating the cams 4 and 5.Although only cams 4 and S'are shown separated by spacers, it will beunderstood that for some applications all of the cams may be arrangedwith such spacers therebetween. The cams and cam spacers are preferablycom prised of an electrically nonconductive material. In order to insurethat the camshaft is strong enough for high voltage and high mechanicalstress applications such as in railway vehicle controllers, the camshaft1 is preferably comprised of a strong rigid material'such as steel. Thesides or faces of the cam elements may include ripples 9, illustrated onthe face-of the cam 2 only, to increase the length of the creepage pathbetween the cam surface andthe central area'of the cam near the shaft.The external surface of the cam spacers 6 through 8 may be I madepreferably large by extending the spacers radially to increase thecreepage path between the adjacent cam elements; y The shaft 1 may besquare so as'to snuglyfit-into square star-shaped or otherwise matchingholes provided in the central portions of the cams. In an alternatearrangement the shaft and holes in the cams may be round and a keyingmeans may be provided in order to secure the cam to the shaft forrotatiomIt is desirable to maintain close tolerances between the holesof the cam elements and the camshaft in order to prevent creepage alongthe camshaft. It will be seen, however, that by means of the presentinvention the requirement for such close tolerances is not as strict asin previous camming arrangements since this invention precludes creepageof conductive fluid to the camshaft. Moreover, since the spacers are notrequired to actuate any switch element, they need not be drivinglyconnected to the shaft.

The central portions of thecams 2 through 5 are provided with extensionmembers or projections adapted to interlock with each other when thecams are placed in adjacent relationship. Taking-the adjacent cams 2 and3 as representative, cam 2 is shown to include an outer projectionmember 10 and an inner projection member 11 while the cam 3 is shown toinclude a center projection member 12 which, when the cams are placed onthe shaft adjacent to each other in operating position, is disposedbetween the projection members 10 and 11. The outer projection member 10is shown in contacting relationship with the face of the cam 3.. Theprojection inner member 11 is disposed in noncontacting relationshipwith the face of the cam 3 so that a cavity 13 is formed between thelower surface of the projection member 12,'the side surface of theprojection member 11, the face surface of the cam 3, and the camshaft 1.In a like manner, the projection member 12 is spaced away from the faceof the cam 2 to form a cavity 14.

The interior faces of the two adjacent cams 3 and 4 are similarlyconstructed in an interlocking fashion. Thus an outer projection member15 and an inner projection member 16 of the cam 3 interlock with acentral projection member 17 provided on the cam 4. The interlockingnature of these two cams are such that the cavity 18 is formed adjacentto camshaft 1 and a cavity 19 is formed adjacent the central projectionmember 17.

The three spaced members 6, 7, and 8 between the cams 4 and are shownwith interlocking projection members which engage each other incontacting relationship. The hollow cores of the cam spacers aredimensioned so as to form a cavity 29 when assembled on the.

camshaft 1. An outer projection member 20 and an inner projection member21 of the cam 4 interlock with a central projection member 22 of the camspacer 6 to form a cavity 23 adjacent the side surface of the projectionmember 22. A central projection member 24 of the earn 5 interlocks withan outer projection member 25 of the cam spacer 8 in contactingrelationship. The lower surface of the projection member 24 and the sidesurface of the cam 5 form the upper-right and right boundaries for thecavity 29. As .may be seen the cam spacers are held in assembledposition away from the camshaft by virtue of the support provided by theprojection member 21 of cam 4 and the projection member 24 of cam 5.

At the left end of the camshaft 1 as shown in FIGURE 1 a plug member 26is shown in interlocking engagement with the cam 2 and a similar plugmember 27 is shown at the right end of the camshaft 1 in interlockingengagement with the cam 5. The extensions of the camshaft 1 beyondeither the plug members 26 or the plug member 27 may engage withhearings or a camshaft driving means which, for simplicity, is notshown.

Froman inspection of FIGURE 1 and with reference.

to the above description it is apparent that the general scheme of thecams, cam spacers, and the camshaft provides the formation of interiorcavities as illustrated by the cavities 13, 18, and 29 adjacentthecamshaft 1, and center cavities 14, 19, and 23, adjacent the sidesurfaces of the central projection members 12, 17, and 22. Each interiorcavity such as 13 has associated therewith a central cavity member suchas 14 disposed to its left and positioned away from the camshaft 1 suchthat communication between the associated cavities exists only betweenthe contacting junction between the central projection member of theright hand cam element and the inner projection member of the left handcam element. It will be apparent that additional cam and cam spacersthan those shown in FIGURE 1 may be employed by positioning them alongthe camshaft 1 as required and that their projection members and cavityarrangements will be sub stantially similar to those shown.

In a preferred embodiment of the species shown in FIGURE 1,'the cavitiesare filled with an insulating sealant, such as silicone rubber, siliconegrease or other suitable electrical insulating composition. The sealantmay be in liquid form when it is poured into the cavities during themanufacture of the camming arrangement. After the manufacture iscompleted, however, the sealant material may remain a liquid or it mayharden. In either case, however, the sealant forms a positivesealvthereby blocking creepage down the faces of the cam elements.

When a hardening type sealant is employed, the inter locking nature ofthe cams and cam spacers and the hard- 4 ened sealant in the cavitiesformed between the interlocking elements tend to add stiffness to thecamshaft 1 which is extremely desirable when greater pressures arerequired between the cams and the switching means (not shown) beingactuated, which conditions may often occur in the electrical control ofrailway vehicle equipment.

In a preferred method of making thecamshaft and carnming arrangement asshown in FIGURE 1, the right end of the camshaft 1 including the plug 27is positioned downwardly so that the camshaft 1 extends upward from thatend. The plug 27 is inserted over the camshaft 1 and is slid down thecamshaft until it reaches its desired position on the shaft as shown inFIGURE 1. The plug 27 is then secured to the camshaft 1 at this positionby any suitable means. Next the cam 5 is slid. onto the shaft followedby the spacers 8, 7 and 6 in that order so that the three sides of thecavity 29 are formed with the fourth and open side being at the top. Thesealant material, which may be in liquid form at this time, is thenpoured into this cavity -until it is substantially filled. Next the cam4 is slid down the camshaft 1 until it begins to interlock with thespacer 6. As the interior projection member 21 of thecam 4 enters thecavity 29, it will begin to displace a portion of the liquid sealantmaterial equal to the volume of that portion of the projection member21-that is inserted ,into the cavity 29. The liquid sealant ma terialthus displaced is forced between the projection member 21 and theprojection member 22 into the center cavity 23. The volume of the centercavity 23 is chosen to be almost equal to or slightly greater than thevolume of the sealant material displaced therein so that all, or atleast most all of the volume of the cavity 23 becomes filled with thesealant when the cam 4 is firmly in place. In assembling the camspacersand cams in the manner described, a small portion of the sealantmaterial may become forced between contacting surface of the cam spacersand between contacting surfaces of the cams. This, however, does notdetract from the effectiveness of the assembly but rather furtherinsures that the creepage path of the conductive dust is effectivelysealed off. The rest of the camshaft assembly is made in a similarmanner as described until the entire assembly is completed. The upperend of the camshaft 1 is then terminated with the plug 26. In order toinsure that the'seal formed between adjacent cam members and between theexterior portions of the cam and the camshaft 1 is maintained effective,it is necessary that no voids or open spaces form between the sealantmaterial and the boundary surfaces of the internal cavities. Thus, thesealant material should be chosen such that as it hardens it does notcontact excessively. Also, it is desirable that the sealant does notcrack as it hardens but rather remains relatively flexible. Siliconerubber and epoxy resin materials have been found to be particularlysuitable for this purpose.

In FIGURE 2 there is illustrated a portion of a cam arrangament for arevolving cam electric switch constructed in accordance with anotherembodiment of the invention. As shown, the required positive sealbetween adjacent cam elements for blocking the formation of anelectrical creepage path to the shaft 1 is provided by one or moreresilient members 30 of a suitable electrically material.

To this end each of the cam elements shown as earns 32, 33 and 34: areprovided with one ormore annular grooves 36 in the opposite sidesthereof. The grooves are so arranged that grooves of adjacent cams orspacers register with each other to form an annular cavity betweenadjacent cam elements. The resilient member 30 is dimensioned so that itwill be tightly retained within the annular cavity'to effect thepositive seal between adjacent cam elements. Conveniently, resilientmember 30 may be a seal of the well known O-ring type. When such O-ringtype seal is employed tight compression thereof in the annular cavitythereof may be provided by selecting an O-ring type seal having aninside and an outside diameter which are slightly larger than inside andoutside diameters of the annular cavity.

In the embodiment illustrated in FIGURE 3 the cam elements are shown asbeing of the interlocking type with the resilient member 30 providingthe required seal as in the arrangement of FIGURE 2. As shown, one ormore such resilient members 30 may be employed and may be located as inFIGURE 2 in the cavity formed by registering grooves in the sides ofadjacent cam elements, or in the cavity formed by registering grooves inthe interlocking portions of the cam elements. Again, the resilientmember 30 may be an O-ring type seal.

Although for purposes of illustration several resilient members 30 areshown interposed in the cavities formed between adjacent cam elements,one such member is all that is required for most applications. ResilientO-ring seals are well known and are commercially available in a widevariety of sizes and cross sectional diameters as well as of variousmaterials the selection of which will depend to some extent upon theexpected operating environment of the switch.

Since member 30 is retained tightly, and preferably compressed, in theannular cavity formed between adjacent cam elements and since it is alsoresilient, it provides a positive seal between adjacent cam elements inspite of shrinkage or other aging effects of the cam elements. Althoughnot illustrated, it is often desirable to provide a coil spring means atone end of the cam element assembly to urge the elements together tominimize the effects of shrinkage or aging of the cam elements.

From the foregoing description it is apparent that the arrangement ofthis invention allows for the use of individual cam elements which maybe arranged in adjacent order to provide a variety of differentswitching arrangements with ease of repair, replacement or rearrangementof cam elements while at the same time providing for a positive sealbetween adjacent cam elements to prevent establishment of a conductingpath between the switch being actuated and the shaft upon which the camelements are mounted.

While the camshaft assembly and method for making the same are describedin terms of a preferred embodiment, it should be understood that variousmodifications and arrangements and other methods will be obvious tothose skilled in the art. Thus, it is not intended that applicant belimited to the embodiments described but rather should be entitled tothe full scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. A camming arrangement for an electrical controller comprising:

(a) a camshaft;

(b) a plurality of cams fixedly secured to said camshaft for rotationtherewith; and

(c) sealing means between each set of adjacent cam elements positionedintermediate said camshaft and the outer portions of said cam elements,said sealing means effectively blocking the formation of an electricalcreepage path between said outer portions and said camshaft.

2. A camming arrangement for an electrical controller for reducing thecreepage of conductive dust comprising:

(a) a camshaft;

('b) a plurality of cams fixedly secured to said camshaft for rotationtherewith;

(c) said cams including projections so that adjacent cams interlock wtiheach other by means cf said projections;

((1) said interlocked projections forming cavities in the creepage pathof the conductive dust; and

(e) a sealant disposed in said cavities.

3. The camming arrangement as defined in claim 2 wherein saidinterlocked projections of any pair of adjacent cams form a first andsecond cavity, both of said cavities being in the creepage path of theconductive dust.

4. The camming arrangement as defined in claim 3 wherein said first andsecond cavities are axially displaced from each other but communicatewith each other through a junction between a pair of said interlockingprojections.

5. The camming arrangement as defined in' claim 4 wherein a first one ofsaid pair of interlocking projections is disposed within said firstcavity so as to displace a volume approximately equal to the volume ofsaid second cavity.

6. The camming arrangement as defined in claim 3 wherein said sealantcomprises silicone rubber.

7. A camming arrangement for an electrical controller for reducingcreepage of conductive dust comprising:

(a) a camshaft;

(b) a plurality of cams fixedly secured to said camshaft for rotationtherewith;

(c) a plurality of cam spacers positioned on said camshaft spacing saidearns at desired distances;

(d) said cams and said cam spacers including projections so thatadjacent cams, adjacent cam spacers, and adjacent cams and cam spacersinterlock with each other by means of said projections;

(e) said interlocking projections between adjacent cams and betweenadjacent cams and cam spacers forming cavities in the creepage path ofthe conductive dust; and

(f) a sealant material disposed in said cavities.

8. A camming arrangement as defined in claim 7 wherein said interlockingprojections of any pair of adjacent cams and any adjacent cams and camspacers form a first and second cavity, both of said cavities being inthe creepage path of the conductive dust.

9. The camming arrangement as defined in claim 8 wherein said first andsecond cavities are axially displaced from each other but communicatewith each other through a junction between a pair of said interlockingprojections.

10. The camming arrangement as defined in claim 9 wherein a first one ofsaid pair of interlocking projections is disposed within said firstcavity so as to displace a volume approximately equal to the volume ofsaid second cavity.

11. In a revolving cam electrical switch, the combination comprising:

(a) a shaft having a plurality of electrically nonconducting camelements arranged thereon for rotation with said shaft, each of said camelements having at lease one annular groove in the opposite sidesthereof adapted to register with the similar groove of an adjacent camelement to form an annular cavity be tween said adjacent cam elements;and

(b) a resilient member of electrically insulating material retainedtightly in said annular cavity and operative to provide a positiveannular seal between adjacent cam elements.

12. The revolving cam electrical switch as recited in claim 11 whereinsaid resilient member is an O-ring type seal and the inside and outsidediameters of which are slightly greater than those of said annularcavity so that said seal is compressed tightly within said cavity.

References Cited UNITED STATES PATENTS 5/1957 Moore et a1 200153 6/ 1963Fisher 200-27

1. A CAMMING ARRANGEMENT FOR AN ELECTRICAL CONTROLLER COMPRISING: (A) ACAMSHAFT; (B) A PLURALITY OF CAMS FIXEDLY SECURED TO SAID CAMSHAFT FORROTATION THEREWITH; AND (C) SEALING MEANS BETWEEN EACH SET OF ADJACENTCAM ELEMENTS POSITIONED INTERMEDIATE SAID CAMSHAFT AND THE OUTERPORTIONS OF SAID CAM ELEMENT, SAID SEALING